STEEL BUCKLING RESTRAINED BRACES …Aniello.pdf · “Only-steel” BRBs have some advantages over...

Rete dei Laboratori Universitari di Ingegneria Sismica (Reluis)

Materiali ed Approcci Innovativi per il Progetto in Zona Materiali ed Approcci Innovativi per il Progetto in Zona Sismica e la Mitigazione della VulnerabilitSismica e la Mitigazione della Vulnerabilitàà delle Strutturedelle Strutture

UniversitUniversitàà degli Studi di Salerno degli Studi di Salerno –– Consorzio Consorzio ReLUISReLUIS, , 1212--13 Febbraio 2007 13 Febbraio 2007

STEEL BUCKLING RESTRAINEDRESTRAINED BRACES FOR SEISMIC UPGRADING

OF RC BUILDINGS

M. D’Aniello, G. Della Corte and F.M. Mazzolani

UNIVERSITY of NAPLES “FEDERICO II” – Eng. M. D’Aniello

BBUCKLINGUCKLING RRESTRAINEDESTRAINED BBRACES (RACES (BRBsBRBs))

BRBsBRBs provide complete truss action with the same response both provide complete truss action with the same response both in tension and in compression in tension and in compression

characterized by compact and round hysteresis loopscharacterized by compact and round hysteresis loops


“Only-steel” BRBs have some advantages over “unbonded” braces:a. Only-steel can be designed to be detachable and inspected after each

seismic event and, if necessary, the yielded steel core can be replaced by a new one.

b. A detachable BRB allows maintenance during the life-time.c. Only-steel BRB is lighter than an Unbonded; this implies a technical

and economical advantage during the assembling

Several types of BRBs have been studied, but two main typologies can be distinguish:

1. Unbonded BRBs2. Only-steel BRBs.

BBUCKLINGUCKLING RRESTRAINEDESTRAINED BBRACES (RACES (BRBsBRBs))


1. Experimental phase A:Test on a masonry-infilled RC building seismically retrofitted by BRBs

1.1 Design of BRB system and “push-pull” test on the retrofitted building 1.2 Development and calibration of numerical models1.3 Vulnerability assessment

2. Experimental phase B:Experimental activity on sub-assemblage elements of only-steel BRBs .

2.1 Cyclic tests on sub-assemblage elements2.2 Calibration and characterization of key properties of a special steel built-up BRBs

Research objectivesResearch objectivesThese advantages led to study a special only-steel detachable BRB, to be used for improving the seismic response of existing buildings. A wide experimental program has been planned as a first step:


Experimental phase A: Experimental phase A: FullFull--scale field tests on scale field tests on

Buckling Restrained BracesBuckling Restrained Braces


Two experimental tests, already performed within the ILVA-IDEM project (Mazzolani 2006), can be considered as the starting point of this experimental study.


Scientific Background: Test 1Scientific Background: Test 1


-500-400-300-200-100

0100200300400500

-0.015 -0.01 -0.005 0 0.005 0.01 0.015 0.02Average 1st story drift angle (rad)

Bas

e sh

ear (

kN)

Core fracture



-500-400-300-200-100

0100200300400500

-0.02 -0.01 0 0.01 0.02 0.03 0.04 0.05 0.06Average 1st story drift angle (rad)

Bas

e sh

ear (

kN)

Gusset plate buckling

Local failure of the restraining tube



1st type of BRB: Not detachable 2nd type of BRB: Detachable

1) the BRB internal core was now tapered in a more gradual manner.

2) the two restraining tubes were now joined together by means of bolted stiffened elements, allowing the BRB to be opened for inspection and monitoring

Increase of total clearance with the core and the restraining elements from 1mm (0.5mm for each side) to 2mm (1mm for each side).


Scientific Background: Scientific Background: Comparison between Test 1Comparison between Test 1--Test 2Test 2

0

100

200

300

400

500

0 2 4 6 8 10 12 14 16 18 20 22 24

Average top displacement (cm)

Bas

e Sh

ear (

kN)

Bare RC structure

BRB - Test n.1

BRB - Test n.2

Test interrupted owing to the achievement of the maximum

allowable core excursionTest interrupted owing to the core fracture


Scientific Background: Scientific Background: Comparison between Test 1Comparison between Test 1--Test 2Test 2

N N –– W viewW view

S S –– E view E view

Masonry-infilled RC building


WC

scale 1:100

AIR CONDITIONINGOFFICE

1200

Ground Floor

OFFICE

EN

TRA

NC

E

1850

OFFICEOFFICE

510

615



(-0.50)

(+5.10)

(+0.70)(+0.60)

390

60

(+9.45)

6037

5

885

435

440

Scale 1:100

1270

TRANSVERSE SECTION



(+2.90)

1 2 3 4 5

6 7 8 9 10 11

12 13 14 15 16 17

BRBs arrangement


BRBs arrangement

BRBs are placed at 1° floor

Perimetric masonry infill walls are only in one bay per each building side


BRBs are hidden in the perimetric facing walls

BRBs arrangement


Buckling Restrained brace to be tested

200 200

510 634200

240 13181886 2350

1886 2350

46240 151882

A

A

B

B

PE/Py = 2.13

Lc/L = 0.4

122

90

202

122

90

202

1

11

1

100

1019

10

3726

37

88

19

88

sez. A-A sez. B-B

6310

Inner clearance: 1mm per each side


Task B: Task B: LaboratoryLaboratory teststests ononOnlyOnly--steelsteel BRB BRB specimensspecimens



Laboratory tests on BRB specimensLaboratory tests on BRB specimens

Starting from the previous BRB, called type 3, a set of one-half scaled BRB specimens will be tested in order to validate this system.In particular, four sub-types will be investigated

3066

23107 75954

1175

255

2543

100

100 100

255317

the sub-type 3a is characterized by the same geometrical proportions of the case type 3

(i.e. the same ratio PE/Py and the same ratio Lc/L )



3066

23107 75954

1175

155

2543

100

100 100

155467

the sub-type 3b differs from the previous one only for thedifferent connection resistance of the two omega profiles

constituting the restraining unit



the sub-type 3c differs from the subtype 3a for a wider clearancebetween the core and the sleeve

(from 1mm per each side to 2mm per each side)

3066

23107 75954

1175

255

2543

100

100 100

255317



the sub-type 3d differs from the first one only in the ratio Lc/L (i.e. its core length ratio is one half of the

ratio for the sub-type 3a)

3066

23107 104854

588

255

2543

100

100 100

255317


ConclusionsConclusions

-In order to develop an innovative “only-steel” detachableBRB, an experimental campaign has been planned.-There are two parts of the experimental program:

1) full-scale tests of existing reinforced concrete (RC) structures equipped with BRBs;

2) laboratory tests

-The full-scale test will be carried out to examine the response of a BRB designed to improve the seismic performance of a real two-story RC building.

-In particular, this BRB was designed to be hidden in the inner hole of facing walls.


ConclusionsConclusions

-The prototypes to be studied in lab tests are scaled version of the BRB designed for the full scale test.

-These specimens will be useful to correctly design the following key aspects:

1. inner clearance giving an understanding on how the clearance width can influence the number of higher-modes in the yielding core.

2. the strength of sleeve connections.

3. the strength of BRB end-connections.


STEEL BUCKLING RESTRAINED BRACES …Aniello.pdf · “Only-steel” BRBs have some advantages over...

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